This invention relates to apparatus for mixing and dispensing a plurality of fluids, especially liquids which react with each other. It is particularly useful as a device for mixing and dispensing polyurethane foam reactants.
There is substantial need for apparatus to produce a uniform homogeneous mixture of a plurality of liquids. In particular, the preparation of polyurethane foams requires the uniform mixing of liquid organic resins with polyisocyanates and the like which react relatively rapidly to form foam. Any mixing of the reactants within the dispensing gun but outside the mixing chamber thereof is most undesirable. Serious problems occur when mixing and reaction take place within the gun but outside of the mixing chamber. The mixture, upon foaming, increases in volume to such an extent that not only are passages within the gun blocked, but also ancillary feed hoses leading to the gun can also be blocked. Thus, not only is the dispensing gun disabled, but hoses leading to the gun often require replacement. This leads to excessive down-time of the gun and economic waste.
In the present invention, as will be evident as this description proceeds, the foregoing problems are substantially alleviated.
U.S. Pat. No. 3,687,370, "Liquid Mixing and Dispensing Apparatus", issued Aug. 29, 1972, and U.S. Pat. No. 4,023,733 "Foam Dispensing Apparatus" issued May 17, 1977, owned by the assignee hereof, disclose a gun-type apparatus for mixing and dispensing a plurality of liquids which is particularly suitable for use with polyurethane foams. The separate liquids are fed under pressure into ports in the forward section of the gun and said ports in turn feed the reactants into a central mixing chamber. Flow into the mixing chamber is controlled by a valving rod. In the past undesired flow around the exterior of the mixing chamber was restrained by inserting the nylon or Teflon mixing chamber into the slightly smaller diameter bore of the metal gun creating a press fit seal. It has been found that such press fit seal is sometimes inadequate to restrain flow of liquids under relatively high pressure and at intermittant flow. With migration, as noted above, the fluids can mix in the passages of the forward section of the gun or around the mixing chamber thereby disabling the gun and requiring replacement of the hoses.
The present invention represents an improvement over the teachings and disclosures of U.S. Pat. No. 3,687,370 and U.S. Pat. No. 4,023,733 as will be apparent from this description. The basic operation and structure of this dispenser is substantially the same as the device described in said patent, and accordingly the disclosure thereof is incorporated by reference herein.